1. Field of the Invention
The subject invention pertains to the art of radar detection and more specifically to radar detection systems wherein the detection threshold is adjusted in accordance to the background noise and interference.
2. Description of the Prior Art
A number of detection techniques for radar, sonar and other detection systems have been proposed in which the detection threshold is automatically adjusted in accordance with variations in background noise and interference. These systems include rank sum, rank quantization and unknown level detection. A rank sum detector passes a video signal through a tapped delay line, whereon the mean signal amplitude, determined over a range cell interval at each tap represents the return signal for a given range cell and on which the presence of a target is sought in the range cell represented by the central tap. The rank of the central tap is determined by comparing the mean signal amplitude at the central tap to the mean signal amplitude at each of the other taps. The rank of the central tap is the number of range cells, in a given group of range cells wherein the mean amplitude is less than the mean amplitude in the range cell represented by the central tap. A target is declared, for the range cell represented by the central tap, when the sum of the ranks obtained after several range sweeps exceeds a specified threshold.
The rank quantization detector like the rank sum detector compares the signal level at the center tap of a tapped delay line to the signal levels at all the other taps. However, instead of obtaining a rank sum after a number of transmitted pulses and comparing the rank sum to a given threshold, the rank quantization detector compares the rank obtained after each transmitted pulse to a specified threshold, sums the number of ranks exceeding the threshold after a number of transmitted pulses and compares the sum to a second threshold to determine the presence of a target.
The unknown level detector also employs a tapped delay line whereon the range cell represented by the central tap is the one of interest. In this detector the square of the mean of the return signal, determined over a range cell interval, at the central tap is compared to the average of the sum of the squares of the mean of the return signals at all the other taps and a hit or a miss is declared, after each transmitted pulse, when the ratio of the square of the mean signal at the center tap to the average of the squares of the mean signals at all the other taps exceeds a specified threshold. As in the rank quantization detector a target report is given when the sum of the hits obtained after a number of transmitted pulses exceeds a given threshold.
Prior art systems provide approximately the same levels of performance and require complex circuitry and an appreciable number of components to achieve a desired probability of target detection. The present invention provides a detection system, which is adjustable to background noise and interference, that realizes a significant reduction in complexity and the number of required components while matching or exceeding the levels of performance achieved by the prior art systems.